A novel computer based method of kinetic analysis will be employed to analyze single injection tracer disappearance curves in terms of the distribution of recirculation times for exchangeable thyroxine and tri-iodothyronine. Studies will be carried out in normals and patient with decreased serum iodothyronine binding to determine whether, as postulated, decreased binding diminishes the proportions of total exchangeable thyroid hormones in tissues, such as muscle, which have slow recirculation times. Studies of the nuclear triiodothyronine receptor complex will focus on the relation of nuclear T3 receptor content to metabolic status and effects of triiodothyronine on nuclear nonhistone protein phosphorylation.